This is a package that allows conversion to and from data in Javascript object notation (JSON) format. This allows R objects to be inserted into Javascript/ECMAScript/ActionScript code and allows R programmers to read and convert JSON content to R objects. This is an alternative to rjson package. That version is too slow for large data and not extensible, but a very useful prototype. This package uses methods, vectorized operations and C code and callbacks to R functions for deserializing JSON objects to R. In the future, we will implement the deserialization in C. There are some routines that can be used now for particular array types.